The present invention relates to a transparent functional membrane wherein functional ultrafine particles having various functions, such as a UV screening effect, an antistatic effect, and an antireflection effect, are localized in a coating, particularly localized and fixed in a coating on its surface layer in contact with or near air, thereby enabling the functions of the functional ultrafine particles to be developed, a transparent functional film, and a process for producing the same. Further, the present invention relates to an antireflection film comprising the above transparent functional film having an antireflection effect, and a process for producing the same.
It is known that a transparent functional film having functions, such as a UV screening property, an antistatic property, or an antireflection property, can be produced by coating on a transparent plastic substrate film a transparent resin composition with functional ultrafine particles having particular properties, such as a UV screening effect, an antistatic effect, and an antireflection effect, being dispersed therein, thereby forming a functional coating.
Further, it is also known that, in order to impart additional properties, such as scratch resistance and chemical resistance, to the above transparent functional film, a transparent functional film having a hard property can be produced by forming as an intermediate layer a hard coat layer of, for example, an ionizing radiation curing resin on a transparent plastic substrate film and coating thereon a transparent resin composition with functional ultrafine particles being dispersed therein.
In the transparent functional film containing the above functional ultrafine particles, the functional ultrafine particles are present in a dispersed form in a transparent functional membrane due to the nature of the process. The incorporation of a larger amount of functional ultrafine particles in the membrane can further enhance the function of the functional ultrafine particles. In this case, however, the filling ratio of the functional ultrafine particles dispersed in the resin should be increased, making it difficult to form a film. Further, the transparent functional film having a hard coat layer of an ionizing radiation curing resin or the like has a problem that the adhesion between the hard coat layer and the transparent functional membrane is so low that the transparent functional membrane is likely to peel off.
The present invention can be divided into three groups A, B, and C which will now be described one by one.
An object of the present invention belonging to group A is to provide a transparent functional membrane, wherein functional ultrafine particles are localized in a high density as a functional ultrafine particle layer in a hard coat layer, thereby enabling the functions of the functional ultrafine particles to be developed and, at the same time, the hard coat layer and the functional ultrafine particles to have excellent adhesion to each other, a transparent functional film, an antireflection film, and process for producing the same.
Another object of the present invention is to provide an antireflection film comprising a transparent functional film having an antireflection effect and a process for producing the same.
The first transparent functional membrane of the present invention comprises a hard coat layer and functional ultrafine particles localized in and fixed to said hard coat layer on the side of at least one surface thereof in contact with an external atmosphere.
The second transparent functional membrane comprises a hard coat layer and functional ultrafine particles localized in and fixed to said hard coat layer on the side of at least one surface thereof in contact with an external atmosphere, a thin film of said hard coat layer being absent in the functional ultrafine particles in their portions in contact with an air layer (an external atmosphere) to cause part of the functional ultrafine particles to be exposed particularly on the hard coat layer.
The transparent functional films of the present invention respectively comprise the first and second transparent functional membranes each formed on a transparent plastic substrate film.
The first process for producing the first and second transparent functional films comprises the steps of: (1) forming a layer of functional ultrafine particles on a release film; (2) coating on a transparent plastic substrate film a resin composition for a hard coat layer; (3) laminating, by press-bonding, the coated transparent plastic substrate film prepared in said step (2), as such, when said resin composition for a hard coat layer contains no solvent, or after removing a solvent when said resin composition for a hard coat layer contains a solvent as a diluent, to the coated release film prepared in said step (1) so that the layer of functional ultrafine particles on the release film faces the resin composition coating for a hard coat layer on said transparent plastic substrate film, thereby causing said layer of functional ultrafine particles to be entirely or partly embedded in said resin composition coating for a hard coat layer; and (4) full curing said laminate prepared in said step (3) and peeling off said release film to transfer said layer of functional ultrafine particles to said transparent plastic substrate film.
Further, the present invention include other embodiment of the above production process, which will be described in detail later.
The present invention belonging to group B relates to an antireflection sheet having the effect of preventing reflection at various displays of word processors, computers, and television, surfaces of polarizing plates used in liquid crystal displays, optical lenses, such as sun glass lenses of transparent plastics, lenses of eyeglasses, finder lenses for cameras, covers for various instruments, and surfaces of window glasses of automobiles and electric railcars.
Transparent substrates, such as glasses and plastics, are used in curve mirrors, back mirrors, goggles, window glasses, displays of personal computers and word processors, and other various commercial displays. When visual information, such as objects, letters, and figure, is observed through these transparent substrates or, in the case of mirrors, when an image from a reflecting layer is observed through the transparent substrates, light reflects at the surface of the transparent substrates, making it difficult to see the visual information through the transparent substrates.
Conventional methods for antireflection of light include, for example, a method wherein an antireflection coating is coated on the surface of glass or plastics, a method wherein a very thin film of MgF2 or the like having a thickness of about 0.1 xcexcm or a metal deposited film is provided on the surface of a transparent substrate, such as glass, a method wherein an ionizing radiation curing resin is coated on the surface of plastics, such as plastic lenses, and a film of SiO2 or MgF2 is formed thereon by vapor deposition, and a method wherein a coating having a low refractive index is formed on a cured film of an ionizing radiation curing resin.
It is already known that, when incident light perpendicularly enters a thin film, in order for the antireflection film to prevent the reflection of light by 100% and to pass light by 100% therethrough, relationships represented by the equations (1) and (2) should be met (see xe2x80x9cScience Libraryxe2x80x9d Physics=9 xe2x80x9cOptics,xe2x80x9d pp.70-72, 1980, Science Sha Ltd., Japan).
n0={square root over (ng+L )}xe2x80x83xe2x80x83equation (1)
n0h=xcex0/4xe2x80x83xe2x80x83equation (2)
wherein xcex0 represents a particular wavelength, n0 represents the refractive index of the antireflection film at this wavelength, h represents the thickness of the antireflection film, and ng represents the refractive index of the substrate.
It is already known that the refractive index ng of glass is about 1.5, the refractive index no of an MgF2 film is 1.38 and the wavelength xcex0 of incident light is 5500 xc3x85 (reference). When these values are substituted in the equation (2), the results of calculation show that the thickness h of the antireflection film is about 0.1 xcexcm in terms of the optimal thickness.
From equation (1), it is apparent that the reflection of light by 100% can be attained by the selection of such a material that the refractive index of the upper coating is equal to a value of square root of the refractive index of the lower coating. The antireflection of light by utilizing the above principle, i.e., by making the refractive index of the upper coating slightly lower than the refractive index of the lower coating, has hitherto been carried out in the art.
In the case of the conventional antireflection sheet with a layer having a low refractive index being formed on the uppermost surface of a transparent substrate film, thickness of the layer having a low refractive index is as small as 0.1 xcexcm, so that the formed antireflection sheet has a poor hard property, resulting in poor resistance to scratch. A hard property has hitherto been imparted to the antireflection sheet by coating a thermosetting resin or an ionizing radiation curing resin on a transparent substrate film, curing the coating, and forming thereon a layer having a low refractive index.
The conventional curable resin layer for forming a hard coat layer has a high crosslinking density, so that the internal cohesion of the coating is high, resulting in poor adhesion between the coating and a plastic film or a sheet as the transparent substrate film. Therefore, it is difficult to say that the above assembly has excellent durability as a conventional antireflection film which also has a surface protecting property. For example, the antireflection sheet, after elapse of a long period of time, causes cracking of the hard coat layer or falling of the coating of the hard coat layer. Further, since the adhesion is poor, the coating is likely to peel off and, at the same time, is less resistant to scratch.
In the production of an antireflection film by successively forming on a transparent substrate film a hard coat layer, a layer having a high refractive index, a layer having a low refractive index, and the like, the transparent substrate film as the first layer of the final product, i.e., an antireflection film, is likely to be damaged in each step, which has an adverse effect on the completion of the final product.
When a layer of an ionizing radiation curing resin is laminated in an uncured state on a transparent substrate film as the first layer of an antireflection film as the final product, followed by irradiation with UV or an electron beam to cure the coating, thereby forming a hard coat layer, the transparent substrate film is unfavorably colored due to irradiation with UV or an electron beam.
Accordingly, an object of the present invention is to provide an antireflection sheet, which is durable, i.e., causes neither cracking nor falling of the coating even after use for a long period of time, resistant to scratch, and less likely to cause damage to a transparent substrate film and coloring during the production of an antireflection film, and a process for producing the same.
In order to solve the above problems, the process for producing an antireflection sheet according to the present invention belonging to group B comprises the steps of: (1) forming or not forming on a release film at least one layer having a higher refractive index than a hard coat layer described below; (2) forming a hard coat layer; (3) laminating said hard coat layer to a transparent substrate film through an adhesive; (4) peeling off said release film from the resultant laminate; and (5) forming on said layer having a high refractive index or said hard coat layer a layer having a lower refractive index than said hard coat layer.
Another process for producing an antireflection sheet according to the present invention comprises the steps of: (1) forming on a release film a layer having a lower refractive index than a hard coat layer described below; (2) forming or not forming on the layer having a low refractive index at least one layer having a higher refractive index than a hard layer described below; (3) forming a hard coat layer; (4) laminating the layers on said release film to a transparent substrate film through an adhesive; and (5) peeling off said release film from the resultant laminate.
The present invention belonging to group C provides a transparent functional membrane wherein functional ultrafine particles having various functions, such as a UV screening effect, an antistatic effect, and an antireflection effect, are incorporated in a coating, particularly localized and fixed in a coating on its surface layer in contact with air by aggregating a plurality of types of functional ultrafine particles, thereby enabling the functions of the functional ultrafine particles to be developed, a transparent functional film, and a process for producing the same.
It is known that a transparent functional film having functions, such as a UV screening property, an antistatic property or an antireflection property, can be produced by coating on a transparent plastic substrate film a transparent resin composition with functional ultrafine particles having particular properties, such as a UV screening effect, an antistatic effect, and an antireflection effect, being dispersed therein, thereby forming a functional coating.
In the transparent functional film containing functional ultrafine particles, functional ultrafine particles are present in a dispersed form in a transparent functional membrane due to the nature of the process. The incorporation of a larger amount of functional ultrafine particles in the membrane can further enhance the function of the functional ultrafine particles. In this case, however, the filling ratio of the functional ultrafine particles dispersed in the resin should be increased, making it difficult to form a film.
In particular, in order to prepare a transparent functional film having an antireflection effect, the transparent functional film should be formed by a plurality of layers having different refractive indexes. The refractive index of each layer can be regulated by incorporating ultrafine particles having a different refractive index. However, the dispersion of a large amount of ultrafine particles in the resin makes it difficult to form a film.
Accordingly, an object of the present invention is to provide a transparent functional membrane, a transparent functional film, and a process for producing the same, which can sufficiently develop the functions of a plurality of types of functional ultrafine particles, enhance the filling ratio of the functional ultrafine particles in the resin for forming a functional membrane and have an excellent adhesion among functional ultrafine particles.
In order to attain the above object, the transparent functional membrane according to the present invention comprises (1) a functional ultrafine particle layer having a multilayer structure, two or more layers constituting said functional ultrafine particle layer being integrated with each other and comprising respective separate aggregates of two or more types of functional ultrafine particles or comprising respective aggregates of two or more types of functional ultrafine particles partly mixed with each other, (2) said functional ultrafine particle layer having a multilayer structure being in contact with a resin layer and localized in and fixed to said resin layer in a region ranging from the interface of said functional ultrafine particle layer and said resin layer to the interior of said resin layer.
The transparent functional film of the present invention comprises a transparent plastic substrate film and provided thereon the transparent functional membrane.